For the past several decades, engineers have worked to develop apparatus and methods to effectively transmit information from components located downhole on oil and gas drilling strings to the ground's surface. Part of the difficulty comes from the fact that the operating environment for the transmission system can be extremely harsh, including temperatures as high as 200° C., pressures as high as 25,000 psi, and extremely abrasive and chemically corrosive conditions.
Another source of difficulty comes from the fact that a drill string may be made up of hundreds of components, such as sections of drill pipe and various downhole tools. Thus, if a data transmission system is integrated into each of these components, it must be capable of connections that can reliably transmit information across the joints among these components.
Moreover, since these components are connected serially to create the drill string that may stretch for thousands of feet below the earth's surface, reliability is imperative. A failure of a single component in the transmission system can bring the whole system down and require an expensive “roundtrip” of the drill string to replace the defective component.
This invention relates to oil and gas drilling and production, specifically downhole components that are part of a drill string and are adapted to house data transmission elements. Disclosed in U.S. Pat. No. 6,670,880, which is incorporated herein by reference, is such a downhole transmission system that transmits data through a string of downhole components. In one aspect of the '880 patent, each downhole component comprises a pin and a box end. The pin end of the downhole components are adapted to be connected to the box end of another downhole component. Each pin end comprises external threads tapering to a pin nose face, pin end secondary shoulder, or mating surface and each box end comprising internal threads tapering to an internal face, secondary shoulder, or mating surface. The pin nose face and the internal face are aligned with and proximate each other when the pin end of one component is threaded into a box end of another component. A data transmission element is located in a cavity in each pin and box end secondary shoulder, the data transmission element being part of the downhole transmission system.
In general, drilling mud or lubricants trapped within a void formed between the threads and secondary shoulders of the pin and box end of downhole components may create high pressure within this region of the tool joints during “make-up” of two drilling components, i.e. when two drilling components are torqued together. High-pressure potentially damages data transmission elements, sealing rings, or other devices disposed in cavities within the secondary shoulders of tool joints. Mud or lubricants on the tapered threads may result in a build up of pressure adjacent the transmission element or sealing ring when the downhole tool strings are made up. The high pressure may force such a device from its cavity and into the tool joint. When the shoulders of the pin and box end are brought together the dislodged device may be sandwiched between the pin and box end secondary shoulders and damaged. The damaged device may further complicate the operation of the downhole tool string by disrupting the transmission system and/or creating leaks paths to the external surface of the tool joint.
Further, torsional forces cause mechanical stress in tool joints. Trapped fluids between the faces of the pin end and the shoulder of the box end may increase the stress applied to the threaded portion or other components of these connections when under torsional stress. If a drill string encounters obstructions while drilling, additional torsional stress can be applied to the tool joints. Further, when drilling horizontally or when drilling through curved sections of the well bore the outer surface of the drill string may rub against the wall of the well bore. This creates additional friction, and passes even more torsional stress to the tool joints. Eliminating any fluids trapped in the void between the pin face and the shoulder face of the box end may prevent a build up of pressure which may lead to failure in certain functions of the tool joint such as data transmission, attachment, and the prevention of fluids leaking outside of the drill string.
In some circumstances the trapped fluid creates enough pressure while making up the tool string that the torque applied at the surface may not be enough to adequately attach the components of the tool string. Torque readings at the surface may indicate that the joint is fully established when in reality the actual torque additional torque is needed because of the resistance caused by the fluid in the tool joint. Further, the extreme temperature in the downhole environment of the well bore increases the temperature in the joint, which in turn increases the pressure within the joint as well.
Attempts to relieve pressure within tool joints of downhole tools strings are well known. U.S. Pat. No. 1,907,522 relates to improvements in joints for rods, more especially to sucker rods used for pumping oil. The '522 patent claims a sucker rod comprising a removable coupling comprising a rod having a socket and provided with a screw thread portion and having a plurality of grooves extending radially through the wall of the socket. The grooves allow for fluid to drain out of the tool joint and into an annulus of the rod.
U.S. Pat. No. 3,822,902 discloses a threaded connection for tubular goods including an externally threaded pin member, an internally threaded box member, and a resilient seal ring positioned between the pin and box members to provide a fluid seal therein. The threaded connection also includes a passage formed in either the pin or box member for conducting thread lubricant or other liquid away from the seal ring as the pin and box members are screwed together. The preferred embodiment of the '902 patent is a flow passage comprising a plurality of longitudinal grooves circumferentially spaced about the pin member and extending transversely though the treads thereof. The longitudinal grooves help prevent a buildup of pressure between the threads of the face of the pin end and the face of the shoulder within the box end of the threaded connection.
U.S. Pat. Nos. 4,750,761; 4,946,201; 6,050,610; 6,442,826; and 6,550,821 disclose other variations of downhole tool joints comprising grooves to relieve pressure between the threads of the pin face and the shoulder face within the box end of downhole threaded connections.
However, specific problems associated with addressing the aforestated difficulties in relieving the pressure generated in connections by making up the joints and trapping the thread lubricant remain in systems having components disposed in cavities in the “pressure zone” have not been addressed by the prior art. These problems are particularly manifested in downhole networking systems employing data transmission elements disposed in cavities within the threaded connections and exposed to the trapped lubricant.